# How weight is scaled.

1. Jun 19, 2012

### DhruvKumar

Every action has equal and opposite action.
There is gravitational force and it pulls us towards it center and A FORCE FROM EARTH is being applied on our body.This is supporting force or Normal force.

Weight is the force of gravity applied on our body by earth and If Earth pulls by X Newton of energy then a force from Earth is also coming of X Newton.
when we stand on Bathroom Scale than our weight is shown by scale .
HOW???
Gravitational force+ Normal force = 0
Then how weight is scaled.

2. Jun 19, 2012

### luis20

I don't know how the bathroom scale works, but you can use a spring and see the length of compression and know your weight since the force applied by the spring is proportional to the compression length

3. Jun 19, 2012

### DhruvKumar

Mr.louis plz read my question and understand it ,then give any answer.

According to Newton's Third Law,
Gravitational force+ Normal force = 0
Then how weight is scaled. As we know Weight is Gravitational force applied on a body by earth.

4. Jun 19, 2012

### azizlwl

Taking downward as positive
Gravitational force - Normal force = 0

As explained by Mr. Lois.
The spring in the scale is compress and the force is -kx.
It is scaled according to x.

5. Jun 19, 2012

### Staff: Mentor

The downward gravitational force (your weight) and the upward normal force are not Newton's third law 'action/reaction' pairs. They happen to add to zero because you are in equilibrium--not accelerating. This is an application of Newton's 2nd law, not the third.
What the scale measures is the normal force it exerts. Which, in this case, happens to equal your weight.